BENDING RIGIDITY OF IONIC SURFACTANT INTERFACES WITH VARIABLE SURFACE-CHARGE DENSITY - THE SALT-FREE CASE

The theoretical understanding of the electrostatic contribution to the bending constants of ionic surfactant interfaces has been extensively developed over the past decade. In this contribution, we deal with sy stems without added electrolyte, and allow for the interfacial charge density to vary with curvature, treating both an undulating sheet geom etry and a spherical/cylindrical cell model. The rippled-plane case sh ows that the lowest free energy state is that for which the surface po tential remains fixed, i.e. a conducting interface. Moreover, the dedu ced expression for the bending modulus agrees with that derived from t he cell model, generalizing our previous result that the bending modul us is geometry-independent, even for systems without added salt, to ca ses where the surface charge is permitted to redistribute on bending. (C) 1997 Elsevier Science B.V.